Corn sees drought stress despite recent rainfall

by Josh Coltrain, Wildcat Extension District Crop Production Agent

Jul 19, 2016

While the old saying may have many different versions, the one I have heard most often is “You’re two weeks from a drought and two hours from a flood.” Due to shallow soils, the water-holding capacity is very low in southeast Kansas. Even with recent rains, corn in our area has experienced varying drought stress. Undoubtedly, this stress has impacted yields but we will not know the extent until harvest.

Corn yield is determined through several components that include ears per area, kernel rows per ear, kernels per row, and kernel weight. Each of these components is molded at specific growth stages.

The ears per area component depends is set during the VE growth. VE is the emergence growth stage (V stands for vegetative). Obviously, the most important factor of this component is emergence and plant population. Even though the seedling is not using much, adequate moisture is necessary for germination and emergence.

Kernel rows per ear are established during the V6 growth stage. In this case, the 6 stands for how many leaf collars are visible on the plant. During this time, the plant uses approximately 0.1 inches of water per day. According to the Parsons Kansas Mesonet site, the average precipitation between March 15 and March 31 was 0.0469 inches per day and between April 1 and April 15, it was only 0.05 inches per day. This suggests that corn in our area could have limited ear girth due to the lack of precipitation during this critical stretch.

During the V12 growth stage, kernels per row are determined. During this stage, the plants are using approximately 0.25 inches of soil moisture per day. Once again, according to the Mesonet, the average precipitation between April 16 and April 30 was 0.267 inches of moisture per day. During this time, moisture should not have been an issue. However, if the corn was late planted, the two weeks between May 1 and May 15 only averaged 0.009 inches of precipitation per day.

Once corn tassels (labelled the VT growth stage), water requirements rise to 0.30 inches per day. By this stage in the growing season, kernels per row have been set. This occurred at the V18 growth stage and during this time, the water is somewhere between the 0.25 required at V12 and the 0.30 required at VT. For Parsons from May 15 to May 31, the average precipitation was 0.309 inches per day which hopefully points to ears with full rows of kernels.

After VT, the plant enters reproductive growth as corn is a determinate plant (all vegetative growth stops once reproduction begins). Silking is the R1 growth stage and during the early reproductive stages, water requirements are maximized. At R1, 0.33 inches of water are needed per day. If we assume this stage occurred in early June, once again at Parsons, the average rainfall was only 0.0847 inches per day from June 1 to June 15. The yield component linked to silking is kernel weight so the lack of moisture during this period suggests smaller kernels.

After silking, the plant progresses through R2 – blister, R3 – milk, R4 – dough, R5 – dent, and finally R6 – physiological maturity. Grain fill occurs from R2 through R5 with a gradual decline in moisture requirements. Drought stress during this time (especially through the milk stage) can lead to kernel abortion limiting the kernels per ear as well. Even the kernels are not aborted, stress can limit grain fill which can make a huge impact on yield. At Parsons, from June 16 to June 30, the precipitation averaged 0.385 inches per day. With any luck, kernel abortion is limited and the plants are actively filling the kernels.

Even though most of our area has received some very welcome rainfall recently, the damage to corn yields may have already occurred. While not nearly as drastic as the drought years in 2010 and 2011, corn yields may not reach the potential we were hoping for at planting.

For more information on corn growth stages, stop by your local extension office for a copy of the new Corn Growth and Development poster. If you have questions or would like more information, please call me at the office 620-724-8233, or email me at jcoltrain@ksu.edu, or visit the Wildcat Extension District website at www.wildcatdistrict.ksu.edu. £

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